Stability of ice-sheet grounding lines

Recent observations of the West Antarctic Ice Sheet document rapid changes in the mass balance of its component glaciers. These observations raise the question of whether changind climatic conditions have triggered a dynamical instability in the ice-sheet-ice-shelf system. The dynamics of marine ice sheets are sensitive to grounding-line position and variation, characteristics that are poorly captured by most current models. We present a theory for grounding-line dynamics in three spatial dimensions and time. Out theory is based on a balance of forces across the grounding line; it is expressed as a differential equation that is analogous to the canonical Stefan condition. We apply this theory to the question of grounding-line stability under conditions of retrograde bed slope in a suite of calculations with different basal topography. A subset of these have based topography inspired by the Pine Island glacier, where basal depth varies in both the along-flow and across-flow directions. Our results indicate that unstable retreat of the grounding line over retrograde beds is a robust feauture of models that evolve based on force balance at the grounding-line. We conclude, based on our simplified model, that unstable grounding-line recession may already be occuring at the Pine Island glacier.The full-text of this article is not available in ORA, but you may be able to access the article via the publisher copy link on this record page